This invention relates to a liquid level sensing switch, particularly a switch in which the switch axis is disposed in a generally horizontal orientation when put to use.
In certain usages of liquid level sensing switches it is desirable for the liquid level sensing switch to be mounted in a sidewall of a container for liquid whose level is to be sensed. This type of mounting may be desirable for any of a number of various reasons, a typical reason being where mounting in a vertical sense cannot be conveniently accomplished.
A horizontal mounting may involve the creation of an aperture in the sidewall of the container for liquid whose level is to be sensed and fitting of the liquid level sensing switch into the aperture. With suitable provisions, the switch can be mounted so that liquid does not leak through the aperture.
In certain instances it is desirable that the aperture be threaded and that the liquid level sensing switch have a corresponding screw thread which allows the switch to be screwed from outside the container into the aperture. Preferably a compressible seal is disposed between the switch and the aperture and compressed to seal the switch to the aperture when the switch is tightened.
Some types of liquid level sensing switches utilize a float which is buoyant in the liquid whose level is to be sensed. So long as liquid level remains above a certain minimum, the float is buoyed upwardly. As the liquid level falls below that minimum, the float assumes a more downwardly position which operates the switch.
Because a liquid level float depends for operation upon the influence of gravity, proper orientation of the float relative to vertical can be important. For a liquid level switch which is to be mounted horizontally, and particularly when it is to be threaded into a threaded aperture in the sidewall of the container, there is no assurance that the final tightened position will produce the required orientation for proper operation of the float for its liquid level sensing purpose.
Special measures can be taken to assure that the switch has been properly oriented. However these special measures might involve procedures, such as trial-and-error shimming, before a satisfactory combination of tightness, sealing, and orientation is achieved. Special measures are generally unacceptable in mass production application, such as in an automotive assembly line, because the line cannot tolerate use of trial and error procedures, or the like, if it is to be operated cost-effectively.
In one respect the present invention is directed to a new and improved liquid level sensing switch which is well-suited for usages, such as in a mass production assembly line, so that a proper orientation of the liquid level sensing float is inherently attained upon the initial installation. In other words, a liquid level sensing switch embodying principles of the invention can be installed and tightened in a threaded aperture in the sidewall of a container so that the proper tightness and leakproofness are attained while there is full assurance that the float assumes an orientation producing proper switch operation regardless of the circumferential orientation of the tightened switch. Moreover, the invention is advantageous in that it can be embodied in a package which is relatively compact, rugged, and well-suited for automotive mass production usage.
The idea of a horizontally disposed level sensing switch is not broadly new. Examples are shown by U.S. Pat. Nos. 3,750,124 and 4,467,156.
The present invention however affords significant improvements over the switches illustrated in those two patents.
The switch of U.S. Pat. No. 4,467,156 comprises an apertured cage which is disposed horizontally within the liquid whose level is to be sensed. A float-mounted contact is captured within the cage and is buoyed when immersed in liquid. When the liquid level drops below a certain minimum level, the contact and float drop so that the contact establishes electrical continuity between the cage and a separate ring which is disposed on the switch in an insulated manner from the cage. This provides a switch closure signal indicative of low level.
Such a device depends on the non-conductivity of the liquid whose level is to be sensed. Moreover, the fact that the contact is contained within the liquid may be deemed undesirable.
The switch of U.S. Pat. No. 3,750,124 comprises a reed switch which is arranged horizontally within the liquid and around which a float-operated magnet is disposed. The float comprises an elongated aperture and it is within this aperture that the reed switch is disposed. The magnet is eccentrically arranged on the float body, as viewed in cross section, and the magnet is embedded centrally within a thicker walled portion of the float.
Moreover, the float is sensitive to the circumferential orientation of the switch mounting on the sidewall of the container. The float is provided with flat outer side surfaces parallel to each other and parallel to the elongation of the aperture. These flat side surfaces confront sideguides on the switch body which guide the float for displacement in the direction of elongation of the aperture. If the sideguides and the flat side surfaces of the float are not substantially vertically disposed, the switch will not perform properly. In other words the switch is sensitive to the circumferential orientation of the switch body in its mounting on the wall of the container.
Furthermore, the switch of U.S. Pat. No. 3,750,124 has a portion of the conductive circuit immersed within liquid in the container, and hence it is susceptible to certain of the same objections as the switch of U.S. Pat. No. 4,467,156.
The present invention is directed in certain of its inventive aspects to a liquid level sensing switch which utilizes a reed switch for the switching device, but with the reed switch and electrical circuit isolated from liquid in the container. Accordingly, the electrical operation of a switch embodying principles of the present invention is unaffected by the nature of the particular liquid material whose level is being sensed.
Briefly, the present invention, in its preferred embodiment, comprises a main body structure which is provided with a screw thread which allows the switch to be threaded into a threaded aperture in the sidewall of a container for liquid whose level is to be sensed. The main body structure comprises a body portion with a circular, cylindrical sidewall bounding an interior space and an endwall which closes the interior space at the distal end. The reed switch is disposed within this interior space in a coaxial manner, and wires extend from leads at the opposite axial ends of the reed switch to an electrical connector at the opposite end of the main body structure via which the switch can be connected with an external electrical circuit. In a particular embodiment of the invention one of the wires may form a coil around the reed switch body so that when the liquid level drops below the minimum level to actuate the switch, the switch is latched in the low level indicating condition.
A float having a circular, cylindrical shape is disposed around the circular, cylindrical sidewall of the switch body portion. The float contains the magnet for operating the reed switch, and in the disclosed embodiment it contains a pendulum weight diametrically opposite the magnet which causes the magnet to vertically overlie the reed switch. Because the float is circumferentially unconstrained by the main body structure, correct orientation of the magnet in overlying relationship to the reed switch is always assured when the switch is installed regardless of the particular circumferential orientation of the main body structure.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawing. The drawing discloses a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.